Method for the direct measurement of pressure differences



Jin. 24, 1967 R, HATSQHEK 3,299,711 0&4,

{ mHOD FOR THE DIRECT IEASUREIENT 0i' PRESSAURB DIFFERENCE-S med Aug.2o. 1963 United States Patent O 3,299,711 Patented Jan. 24, 1961 icc Aer1/ez e aal-a. (cr. '1s-ass) l0 ast a certain amount of accuracy, as isfrequently for the testing ot internal combustion engines is advisableto measure the said ditference directly so as to preclude subsequentdifferences resulttwo individual pressures. According to a conprocess,two quartz transducers of identical sensitivity comprising antipolarquartz columns are being their signals being transmitted to anelcetrometer as a measuring instrument. The inherent drawback o( thisprocess is due to the fact that transducers with quartz columns are notgenerally available in and have therefore, to be custom-built atcouexpense.

According to another known process the individual pressures are measuredby means of homopolar trans ducers using two distinct electrometersteps, the difference, if any, being determined by electronic means at a7 r stage. This arrangement is also uueatiaiaetory inasmuch as pressureditferences have to be measured with the same measuring range asindividual prennes, so that particularly n such cases where minortricaloutput signals corresponding to the individual preseures.According to the invention the output signals of the two transducers sseelectrostrictively transformed into mechanical impulses corresponding tothe pressure ditfenences which are then transduced into au electricalsignal g to the pressure dili'erence either by piezoelectrieormvemeansorbymeansoiapiezoresistance eifect with semi-conductora. Ascompared with conventionall methods using two hornopolar transducerstheproeesasccordingtotheinventionoti'ersthew vamage of considerablygreater accuracy. In addition. complicated electrometer an'angements maybe dispensed with and commercial types of transducers may be used forthe purpose.

According to another feature of the invention an electrestrictive bodyis provided for the practical performance of the method according totheinvention, said body comprising two electrodes, one oi which is loadedby the output signal oi a transducer. inasmuch as consequently. thesignals transmitted by the two electrodes are identical and correspondto the individual pressures, the electroetrictive body is thrown intovibration only it and when the two signals didsr from each other.revealing the presence ol a pressure difference, the mechanical impulsesreduced by the electrostrictive body corresponding exeetly to thepressure dilerencs to be measured. Thus the apparatus according to theinvention distinguishes keel! by its estreme simplicity.

According to a further embodiment of the Invention other pisaneleetriebod may be mechanically coupled wat the slestrostrietlvs hotlycomprising electrodes tor l0 determine minor pressure di'erences withthe electrical signal corresponding to the pressure dilfer ence.According to the invention the electrostrictive and/ or piezoelectricbody may itself comprise two additional electrodes for the transmissionof the electrical signal corresponding to the pressure difference. Bymeam of these equally simple arrangements the mechanical impulsesproduced by the clectrostrctive body are transformable in a simplemanner into an electric signal accurately correo spondng to the pressuredierenoc to be measured. By the selective use of suitable piezoelectricmaterials it is also possible to amplify the electric signals by meansof the system according to the invention utilizing both the longitudinaland the transversal piezoelectric eii'cct.

Further details of the invention will appear from the followingdescription of several embodiments of the invertrc'gn with reference tothe accompanying drawing in w FIGURES l and 2 each show an example of anem bodiment of the invention.

In the embodiment illustrated by FIGURE 1,the output signalscorresponding to the individual pressures are transmitted by thetransducers l and 2 via leads 3 and 4totheelectrodessandofasolidbodyloonsistingoi electrostrictive material.Adjacent to the electrostrietive body 7 is another solid body 8 ofpiezoelectric material presenting electrodes 9 and 1l. The solid bodies7 and 8 are rigidly clamped between two walls ll and l2 and closelyresting against each other with s bias alongside a precision-polishedcontact surface 13. The electrode 9 of the body 8 of piezoelectricmaterial isconuected to the frame, whereas the electrode 10 is connectedvia lead 14 to a measuring instrument, for example an electrometer (notshown).

The two transducers l and 2, illustrated only scite-A matically in theaccompanying drawing are of a commercial type and have been adapted toeach other. Besides the two transducers l and 2 are homopolar, connectedin opposition and directly connected with the two electrodes 5 and 6.Since the latter are not grounded, theinputsignalactingontheelectrostrietivebodylcorrespondstothedilerencebetweenthesignalsofthetramduccrs l and 2 indicating the respective individual preesures.Thirinputsignalistransforrnedbytheelectrostrictive body 'l into amechanical impulse also corrosponcling exactly to the pressure dierenceto be measured. Byrnesnsotthemechanicalcoupiingbetweenthetwobodieslandltheimpulsesaretransmittcdfrornbodyltobodylsothatasaresultot'deformationsloadsareproducedonitssurfacewhichareeollectedbytlmelectrodeaendleandtransrnitsedbythelatterasaa diterence.

electric material. 111e body 15 is also clamped between two walls 1l andl2 and carries the two electrodes 5 and 6 connected with the transducersl vialeads3and4ononeside,andtheclectrodes 10 from which the electricsignal t pressure difference can be collected, on the other sida. Thisarrangement'is simpler than the one using two solid bodies since auchprecautions as have generally to be takentoensurethepropertransmissionotforcebetweeathe solid bodies are not hererequired. Y

In the two embodiments o! the invention ilhtstrated in and by theaccompanying drawing the transversal pisanelectrie effect is beingutilised. However. h is sho poesible, within the scope et the invention,to use nel arrangements aspre operated with the Us ot the lolgitudlnalpiezoelectric eect. Again. the second sold transforming the mechanicalimpulses ot the electrnurie smmrr 4 trial nd oo-opernte with a probe,for example s magl* P050- l coil or the like by means of which the inniis collected. Finally, lt is also possible to use o vnr'utor as thesecond solid body, said varistor consistil. preferably of n singlegermanium or silicon crystal nog also comprising the requiredelectrodes.

l. A method for directly measuring pressure differlo ences, vlllreiupiezoelectric transducers are provided, oompris'n. measuring theindividual pressures by two piezoelectric transducers transmittingoutput signals corresponding to the individuel pressures, transformingthe output signals of the said transducers by elec- 15 hg to the premuradilference, transforming the said impulses into an electric signalcorresponding to the prev uro 2. A method as claimed in claim l, wherebythe said 20 vmechanical impulses are transformed by piezoelectric meansinto an electric signal corresponding to the pressure 4 3. Armetltod asclaimed in claim l, whereby the said mechanical impulses are transformedby electrostrctive means into an electric signal corresponding to thepres sure difference.`

4. A method as claimed in claim l. whereby the said mechanical impulsesare transformed by using the piezo .resistance effect in semiconductorsinto an electric signal corresponding to the pressure dill'erence.

References Cled by the Examiner I n UNITED STATES PATENTS g 1,902,1843/1933 Rieber 73-7l.4 2,767,336 10/ 1956 Arenberg B10-8.3

1. A METHOD FOR DIRECTLY MEASURING PRESSURE DIFFERENCES, WHEREINPIEZOELECTRIC TRANSDUCERS ARE PROVIDED, COMPRISING, MEASURING THEINDIVIDUAL PRESSURES BY TWO HOMOPOLAR PIEZOELECTRIC TRANSDUCERSTRANSMITTING OUTPUT SIGNALS CORRESPONDING TO THE INDIVIDUAL PRESSURES,TRANSFORMING THE OUTPUT SIGNALS OF THE SAID TRANSDUCERS BY ELEC-